A new study from Canada has similar findings to research from Growing Up In New Zealand, of significantly increased problems with attention at age 5 in preschoolers with over 2 hours of screen time per day (including being 7x more likely to exhibit symptoms of ADHD).
"The two big takeaways from this study are that children exposed to more screen time, at either age three or five years, showed significantly greater behavioural and attention problems at age five and this association was greater than any other risk factor we assessed, including sleep, parenting stress, and socioeconomic factors."
"Current Canadian guidelines call for no more than 2 hours screen time a day at that age. But our research suggests that less screen time is even better."
Further research is needed, and authors suggest that up to half an hour of screen time a day is acceptable.